1. Field of the Invention
This invention concerns a coordinate input device and, more in particular, it relates to a structure of a transfer portion with improved reliability of a coordinate input device when used, particularly, under a circumstance in a wide temperature range.
2. Description of the Related Art
In a case where the surface of a flat plate is designated by a coordinate pointer such as a pen or a finger, or a trace is drawn by moving the designated point, a coordinate input device in which a cursor indicates a corresponding coordinate position on a computer display or a cursor is moved to draw a trace is referred to as a tablet and has been used generally.
FIG. 4 shows a first example of an existent structure of a coordinate input device. FIG. 4 is a plan view illustrating a coordinate input device of a first example in an exploded state.
FIG. 4A is a plan view of an upper electrode plate 102 of the coordinate input device of the first example and FIG. 4B is a plan view of a lower electrode plate 103 of the coordinate input device of the first example.
The coordinate input device of the first example shown in FIG. 4 comprises an upper electrode plate 102, a lower electrode plate 103, a flexible printed circuit board (hereinafter simply referred to as FPC) 104 as a connection terminal with a control driving section (not illustrated)
The upper electrode plate 102 shown in FIG. 4A comprises, on a film substrate 100, an ITO (indium tin oxide) resistor layer 105a, a pair of parallel elongated rectangular electrodes 106a and 106b, transfer portions 109a and 109b formed near both ends of the electrodes 106a and 106b and an insulation resist 108a laminated successively.
Further, the lower electrode 103 shown in FIG. 4B comprises, on a glass substrate 101, an ITO resister layer 105b, an insulation spacer (not illustrated), a pair of elongated rectangular electrodes 106c and 106d parallel with each other, wiring patterns 107a-107d, the transfer portions 109c and 109d described above and an insulation resist 108b laminated in this order, to which the FPC 104 is connected.
The electrodes 106a and 106b shown in FIG. 4A are formed along opposing shorter sides of the film substrate 100 respectively, and the insulation resists 108a and 108b are formed along the shorter sides of the substrate 100 so as to cover the electrodes 106a and 106b. 
Further, the insulation resists 108a and 108b are provided with uncovered portions near both ends of the electrodes 106a and 106b and the portions constitute transfer portions 109a and 109b. 
The electrodes 106c and 106d shown in FIG. 4B are formed along opposed longer sides of the glass substrate 101 respectively.
Further, electrodes 106e and 106f are formed along the shorter sides of the glass substrate 101 on the previously formed insulation resist and they are placed at positions corresponding to the electrodes 106a and 106b of the upper electrode 102.
The lower electrode plate 103 shown in FIG. 4B is formed with an insulation resist 108c along four sides thereof, the insulation resist does not cover the portions corresponding to the transfer portions 109a and 109b disposed near both ends of the electrodes 106a and 106b of the upper electrode 102 and the uncovered portions constitute transfer portion 109c and 109d. 
In FIG. 4B, wiring patterns 107c, 107d, 107a and 107b are connected to the right of the electrode 106c, at the right end of the electrode 106d, and the upper ends of the electrodes 106e and 106d, respectively, and the other ends of the wiring patterns 107a to 107d are connected with the FPC 104.
The insulation resist 108c is formed along four sides of the lower electrode plate 103 so as to cover the electrodes 106c to 106f and the wiring patterns 107a to 107d. 
When the coordinate input devices is assembled, the upper electrode plate 102 and the lower electrode plate 103 are joined at the position of opposing the ITO resistor layers 105a and 105b, arranging, the electrodes 106a and the 106c at a right angle, and abutting the transfer portion 109a of the upper electrode plate 102 with the transfer portion 109c of the lower electrode plate 103 and the transfer portion 109b of the upper electrode plate 102 with the lower electrode plate 109d. 
Then, the abutted transfer portions are integrated by heating and solidification.
The circuit from the electrodes 106a to 106d to the FPC 104 shown in FIG. 4 has such a structure that the electrodes 106a and 106b are connected by way of the transfer portions 109a and 109b to the electrodes 106e and 106f provided with the transfer portions 109c and 109d of the lower electrode plate 103 and connected by way of the wiring patterns 107a and 107b of the lower electrode plate 103 to the FPC 104 in the upper electrode plate 102, while the electrodes 106c and 106d are connected by way of the wiring patterns 107c and 107d to the FPC 104 in the lower electrode plate 103.
The coordinate input device described above has been incorporated in mobile equipment and the working conditions have become increasingly severe.
It is necessary that the mobile equipment operate stably over a wide range of temperatures, for example, from xe2x88x9230xc2x0 C. to 70xc2x0 C. and, naturally, it is also necessary for the coordinate input device mounted thereon to secure stable operation in the temperature range described above.
However, in the structure of the existent coordinate input device of the first example described above, since a film substrate is used for the upper electrode plate 102 and the glass substrate is used for the lower electrode plate 103 in order to adopt an advantageous structure in view of the operationability and the durability, a problem exists. In temperatures that are greatly different from the temperature upon bonding both of the electrode plates, stress generated by the difference of the thermal expansion coefficient between the film substrate and the glass substrate and by expansion and shrinkage of an air layer in a space between both of the electrodes is exerted on the transfer portions 109a to 109d connecting the circuits of the upper electrode plate 102 and the lower electrode plate 103 to defoliate the transfer portions and result in disconnection of the connection circuit to the driving control section.
Then, as one of means for solving the problems, it has been known a method of constituting the film substrate used for the upper electrode plate as a two-layer structure formed by appending to film substrates of different thickness.
FIG. 5 shows a partial cross sectional structure of an upper electrode plate 202 using a film substrate of a two-layered structure as a second example of the existent coordinate input device. The upper electrode plate 202 of the second example shown in FIG. 5 has an identical constitution with that of the upper electrode 102 of the first existent example shown in FIG. 4A except for using a film substrate 220 of the two-layered structure.
The upper electrode plate 202 shown in FIG. 5 as a fragmentary cross sectional structure uses a film substrate 221 made of polyethylene terephthalate (hereinafter simply referred to as PET) of 125 xcexcm thickness and a film substrate 222 made of PET of 25 xcexcm thickness bonded and secured to each other by an adhesive 223 of about 25 xcexcm thickness as a film substrate 220, in which an ITO resistor layer 205, an electrode 206, and an insulation resist 208 are formed successively on the side of the film substrate 222 of 25 xcexcm thickness.
The thickness of the film substrate 220 in the upper electrode plate 202 of the second existent example is 175 xcexcm and the thickness of the film substrate 100 used for the upper electrode plate 102 of the first existent example shown in FIG. 4A is also 175 xcexcm.
However, since the film substrate 220 of the second existent example has a two-layered structure, an effect of moderating the stress due to expansion and shrinkage of the film substrate 221 of 125 xcexcm thickness is exerted by the fluidity of the adhesive 223 put between the film substrates 221 and 222.
That is, in the coordinate input device of the second existent example having the upper electrode 202 using the film substrate 220, most of the stress exerted on the transfer portion is from the film substrate 222 of the thickness of 25 xcexcm. In the first existent example shown in FIG. 4, the stress exerting on the transfer portions 109a to 109d is a stress from the film substrate 100 of 175 xcexcm thickness.
When comparing them to each other, it is apparent that the stress exerted on the transfer portions of the coordinate input device of the second existent example is greatly reduced.
Accordingly, in the second existent example, the transfer portions are less defoliated to improve the reliability of the coordinate input device.
However, the film substrate 220 of the two-layered structure described above involves a problem that the structure is complicated and, accordingly, the production cost is high and it is not suitable to the present situation where cost competition becomes more important as mobile equipment becomes more popular and further reduction of cost has been demanded.
In view of the above, as a method of preventing the detamination of the transfer portions with no increased cost as in the film substrate 220 of the two layered structure described above, a method of narrowing the distance of the transfer portions corresponding to the pair of electrodes has been adopted, in order to minimize the effect of the dimensional change on the transfer portions due to expansion and shrinkage of the film substrate.
FIG. 6 and FIG. 7 show a coordinate input device using the method of narrowing the distance between the transfer portions as a third example.
FIG. 6A is a plan view of an upper electrode plate 302 of a coordinate input device as viewed on the side of resistor layer 305a, while FIG. 6B is a plan view of a lower electrode plate 303 of a coordinate input device as viewed on the side of the resistor layer 305b in the third existent example.
Further, FIG. 7 is a view illustrating a fragmentary cross sectional structure of the coordinate input device of the third existent example. For the constituent elements shown in FIG. 7, the constituent elements identical with those shown in FIG. 6 carry the same reference numerals for which explanation is omitted or simplified.
The upper electrode plate 302 of the third existent example shown in FIG. 6A comprises an ITO resistor layer 305a formed on a substrate 302a, elongated rectangular electrodes 306a and the 306b formed along shorter sides of the substrate 302a, a wiring pattern 307, transfer portions 309a and 309b and an insulation resist 308a. 
The lower electrode plate 303 shown in FIG. 6B comprises an ITO resistor layer 305b formed on a substrate 302b, elongated rectangular electrodes 306c and the 306d formed along longer sides of the substrate 302b, a wiring patterns 307c and 307d, transfer portions 309c and 309d and an insulation resist 308b. 
Reference numeral 304 designates an FPC as a connection terminal to a driving control section (not illustrated).
In FIG. 6A, a transfer forming portion 310a is disposed to the upper end of the electrode 306a, the wiring pattern 307 is connected to the upper end of the electrode 306b and a transfer forming portion 310b is disposed to the other end of the wiring pattern.
Further, the insulation resist 308a is formed along four sides of the upper electrode plate 302 so as to cover the electrodes 306a and 306b, the wiring pattern 307 and the transfer forming portions 310a and 310b, but a portion not covered with the insulation resist 308a is disposed at a central portion of each of the transfer portions 310a and 310b and the uncovered portions constitute the transfer portions 309a and 309b. 
In FIG. 6B, wiring patterns 307c and 307d are connected near the right end of the electrode 306c and at the right end of the electrode 306d, respectively.
Further, a transfer forming portion 310c is disposed at the right upper end of the lower electrode plate 303 and a transfer forming portion 310d is disposed at a position rightward to the upper end center of the lower electrode plate 303. The positions correspond respectively to the transfer forming portions 310a and 310b of the upper electrode.
The wiring patterns 307a and 307b are connected respectively to the transfer forming portions 310c and 310d. 
Each of the wiring patterns of the lower electrode 303 is connected with the FPC inserted between the transfer forming portions 310c and 310d. 
An insulation resist is formed along four sides of the lower electrode 303 so as to cover the electrodes 306c and 306d, the wiring patterns 307a to 307d and the transfer forming portions 310c and 310d of the lower electrode 303 shown in FIG. 6B.
However, a portion not covered with the insulation resist is disposed at a central portion of each of the transfer forming portions 310c and 310d at a position corresponding to the transfer portions 309a and 309b of the upper electrode and the uncovered portions constitute the transfer portions 309c and 309d. 
When the coordinate input device of the third existent example shown in FIG. 6B is assembled, the upper electrode plate 302 and the lower electrode plate 303 are joined by opposing the resistor layers 305a and 305b, arranging the electrode 306a and the 306c at a right angle, and at the position of abutting the transfer portion 309a of the upper electrode plate 302 with the transfer portion 309c of the lower electrode plate 303 and the transfer portion 309b of the upper electrode plate 302 with the transfer portion 309d of the lower electrode plate 303.
Then, the abutted transfer portions are integrated by heating and solidification.
FIG. 7 is a view showing a fragmentary cross sectional structure of a coordinate input device of a third existent example, in a state where the lower electrode plate 303 formed by successively laminating the ITO resistor layer 305b, the electrode 306c and the insulation resist 308b on the glass substrate 321 and the upper electrode plate 302 formed by successively laminating the ITO resistor layer 305a, the electrode 306a, and the insulation resist 308a on the film substrate 322 are bonded, with the ITO resistor layers 305a and 305b being opposed to each other.
In the third existent example, the circuit structure to the FPC 304 shown in FIG. 6 is such that the electrodes 306a and 306b are connected by way of the transfer portions 309a and 309b to the transfer portions 309c and 309d and connected by way of the wiring patterns 307a and 307b of the lower electrode plate 103 to the FPC 304 in the upper electrode plate 302, while the electrodes 306c and 306d are connected by way of the wiring patterns 307c and 307d to the FPC 304 in the lower electrode plate 303.
In the coordinate input device of the third existent example, as shown in FIG. 6, since the gap between the transfer portions 309a and 309b is made narrower than the gap between the transfer portions 109a and 109b of the second existent example shown in FIG. 4, the amount of change of the gap in the transfer portion upon expansion and shrinkage of the film substrate can be decreased to reduce the load on the transfer portions 309a and 309b. 
Further, in the coordinate input device of the third existent example, the wiring pattern 307 is formed along one side of the upper electrode plate 302 in order to narrower than the gap between the transfer portions 309a and 309b. 
However, since it is necessary that the equi-potential line formed by the pair of electrodes 306a and 306b is in parallel with the electrodes 306a and 306b upon use of the coordinate input device, the wiring pattern 307 is insulated by the insulation resist 308 from the ITO resistor layer 305a. 
While it is not necessary to form the insulation resist on the upper electrode plate 102 of the first existent example, the insulation resist 308a has to be formed on the upper electrode plate 302 in the third existent example.
In view of the above, the third existent example involves a problem that increase of the manufacturing cost is inevitable due to the increase of the number of steps.
This invention has been accomplished in order to overcome the foregoing problems and intends to provide a coordinate input device capable of preventing delamination of transfer portions and improving the reliability at a reduced cost.
For attaining foregoing object, this invention has the following constitution.
In a coordinate input device according to this invention, a first electrode plate having a resistor layer, a pair of electrodes disposed along opposing two sides of a substrate, a wiring pattern led from the electrodes to the vicinity of other one side, a transfer portion disposed at the top end of the wiring pattern and a second electrode plate having a resistor layer, a pair of electrodes and a wiring pattern are bonded with the surfaces of each of the resistor layers being opposed and with the electrodes being arranged at a right angle to each other wherein a bridge portion through which the wiring pattern passes is disposed near a transfer forming portion of the first electrode plate.
That is, it is designed such that a bridge portion through which the wiring pattern passes is disposed in the midway of a circuit connecting the electrode and the transfer portion in the first electrode plate, thereby separating the electrode plate into a electrode portion and a transfer portion and moderating the stress caused by expansion and shrinkage of the substrate exerting on the transfer portion by the bridge portion and preventing delamination of the transfer portion.
Further, since the equi-potential line parallel with the electrodes formed by the electrode no more undergoes the effect of the electric field by the wiring pattern led out of the electrode by the separation of the electrode portion and the transfer portion by the bridge portion, it is not necessary to cover the wiring pattern as far as the transfer portion with the insulation resist.
Accordingly, since the electrode plate is completed only by the step of forming the resistor layer on the substrate and the step of forming the electrode and the wiring pattern, the cost can be reduced by the simplification of the steps.
Further, the coordinate input device can provide a structure in which the first electrode plate has a concave portion formed on one side of the substrate and convex portions defined with the concave portion on both sides thereof and a transfer portion is disposed on the convex portion.
That is, since the transfer portion is disposed on the convex portions disposed on both ends for one side of the electrode plate, stress for the electrode portion or the transfer portion generated by expansion and shrinkage of the substrate always exerts by way of the bridge portion to other portion constituting the electrode plate.
Accordingly, the stress caused by the expansion and shrinkage is moderated by the bridge portion and the reliability of the transfer portion can be improved further.
Further, the bridge portion connecting the transfer portion and the electrode portion can be formed by disposing a recess to the substrate near the transfer portion.
That is, since a substrate having a shape in which the transfer portion and the electrode portion are separated by the bridge portion can be manufactured by fabricating a shape having a recess near the transfer forming portion in the step of fabricating the substrate into a desired shape, it can avoid increased cost by the addition of steps.